1. Field of the Invention
The present invention relates to log yarding using a load-hoisting carriage traversing a skyline extending over an area from which logs are to be removed.
2. Prior Art
McIntyre U.S. Pat. No. 3,022,747 discloses a "Skyline Yarder With Radio Controls" for downhill logging operations in which a carriage is movable along an inclined skyline by hauling in or paying out a "tow cable" stored on a winch at one end of the skyline and having an end connected to the carriage. A diesel engine is mounted on the carriage for driving a drum containing a "yarding cable" to pay out such cable from the carriage to a hooker on the ground and to haul in such cable to hoist a load of logs hooked by the hooker. Brakes actuated by air cylinders are provided to lock the carriage in a desired position on the skyline and to lock the yarding cable drum after the log load has been hoisted. Radio control mechanism actuates the brake air cylinders, adjusts the speed of the diesel engine and controls the direction of turning of the yarding cable drum.
A problem with the log yarding apparatus of U.S. Pat. No. 3,022,747 is that the skyline must be capable of supporting not only a log load, but also the yarding cable drum, the substantial amount of yarding cable stored on the yarding cable drum, the diesel engine required to turn the drum, a store of fuel for the diesel engine, a storage tank for compressed air for the brake air cylinders and, perhaps, an air compressor. In addition, it often is necessary to refuel the diesel engine and recharge the air storage tank and since the skyline is "at least 40 feet above the ground at all points", access to the engine fuel tank and air storage tank is a problem. Further, complicated clutch mechanism is required so that the engine can drive the yarding cable drum in either direction. Moreover, the radio control mechanism is complicated, including separate controls for actuating the brakes, adjusting the engine speed and actuating turning of the yarding cable drum in either direction. Consequently, the logging apparatus of U.S. Pat. No. 3,022,747 requires frequent maintenance and is heavy, bulky, expensive and difficult to operate.
The "Cable Logging Operation" disclosed in McIntyre U.S. Pat. No. 3,083,839 is similar to the operation disclosed in U.S. Pat. No. 3,022,747, the primary difference being that an "in-haul or snubbing cable" extending from a winch at one end of a skyline and through slack-pulling mechanism on a carriage is substituted for the tow cable and yarding cable of U.S. Pat. No. 3,022,747. The slack-pulling mechanism is operable to pay out from the carriage snubbing cable fed to it by the separate snubbing cable winch on the ground. Such winch, rather than mechanism on the carriage, is used to haul in the snubbing cable to hoist a log road to the carriage.
Similar to the apparatus of patent No. 3,022,747, in the apparatus of patent No. 3,083,839 an internal combustion engine and its fuel tank are mounted on the carriage for powering the slack-pulling mechanism. In addition, air cylinders are provided for actuating brakes for locking the carriage to the skyline and the snubbing cable to the carriage and an air compressor is mounted on the carriage for actuating the brake air cylinders. Further, complicated radio control mechanism is required, including separate controls for actuating each of the brakes and for adjusting the speed of the slack-pulling engine.
Malakhoff U.S. Pat. No. 3,336,878 discloses a "Remote Winch Operated Trolley Hoist" in which a carriage or "trolley" is suspended from a skyline or "high line". A "haul line" extends from a winch at one end of the skyline, around sheaves carried by the carriage and to another stationary winch. A separate hoisting line is carried on a drum on the carriage. Such drum is mechanically driven to pay out and haul in the hoisting line by rotation of the carriage sheaves as the haul line is moved through the carriage. Brakes actuated by hydraulic cylinders are provided to lock the carriage to the skyline and the haul line to the carriage. The brake hydraulic cylinders are powered by hydraulic liquid under pressure stored in an accumulator on the carriage. The accumulator is regenerated by a hydraulic pump driven by movement of the haul line through the carriage.
As with the apparatus of U.S. Pat. No. 3,022,747, a problem with the apparatus of U.S. Pat. No. 3,336,878 is that the skyline must be capable of supporting not only the load hoisted to the carriage, but also the hoisting line drum, the supply of hoisting line stored on the drum and the mechanical drive mechanism for turning the hoisting line drum. In addition, the haul line extends from a winch at one end of the skyline, through the carriage sheave mechanism, through a sheave at the other end of the skyline and back to another winch at the first end of the skyline and, consequently, a long length of haul line and two haul line winches are required.
Other logging systems using carriages mounted on skylines are disclosed in McIntyre et al. U.S. Pat. No. 3,407,942 and Hale et al. U.S. Pat. No. 3,647,255.